The present invention relates to a head-up display unit for use with the face-mask of a self-contained breathing apparatus (SCBA) unit.
Self-contained breathing apparatuses typically comprise a harness, on which is mounted a cylinder of breathable gas under high pressure. The gas is reduced in pressure to a medium pressure at a first stage regulator on leaving the cylinder after which it travels through a hose to a second stage regulator, attached to a face-mask worn by the user. The second-stage regulator reduces the pressure of the gas to a pressure slightly above atmospheric.
It is known to have a head-up display unit in the face-mask that displays to the user the pressure in the gas cylinder. A battery located in the face-mask may power the display unit. For ease of operation it is important that the operation of the head-up display unit is automatic.
A known head-up display unit has two modes, SLEEP and ON. When the unit detects a signal relating to the gas pressure the unit enters the ON mode and the gas pressure is displayed by the unit. If a signal is not detected for a predetermined period of time then the unit enters SLEEP mode. The unit is still powered in this mode but the power consumption is much less. The problem with a unit of this type is that even when it is not being used power is consumed.